(US4891325-A)      Silicon base material (S) of a metal insulator semiconductor (MIS) inversion-layer solar cell, is re-used. A first electrically conductive contact of full-area or partial type is arranged on one side of the base material, and the MIS solar cell-specific layers are arranged on the opposite side. The MIS layers are in the form of a first insulating layer (I), e.g., a silicon oxide layer; a second electrically conductive contact (M), provided on layer (I), and designed pref. in finger or lattice form; and a further insulating layer, e.g., a silicon nitride or silicon oxynitride layer.    The improvement is that at least MIS solar cell-specific layers, in the form of the second insulating layer and the second electrically conductive contact, are stripped off and replaced by corresp. new layers.    ADVANTAGE -   New silicon base material re-use method is provided which is cheap and technically simple. (5pp)i    (DE3871456-G)      The cell is constructed as follows: on a p-Si substrate (12) a contact (24) is formed on the back surface. On the front-surface are a first SiO2-insulation layer (14), contacts (18) and a second dielectric layer (16) of Si-nitride or oxynitride. During reworking at least the second dielectric layer (16) and front-contacts (18) are removed and replaced by corresponding new layers. Pref. the alkali-ions (22) e.g. Cs, contained in the first dielectric layer (14) are removed.    The removal of the layers is selectively and a chemical or plasma-chemical etch-process is used. The second dielectric layer is removed first, then both contact-layers at the same time, pref. by using a mineral acid e.g. o-phosphoric acid, by immersion at 50-100 deg.C. The contacts may also be plamsa-etched using Cl2. The 2nd dielectric layer is pref. removed by plasma-etching using C2H6 + O2 or NF3. The metal-layer (18) and 2nd dielectric layer may also be removed by mechanical means.    Also claimed is reforming of the solar cell by formation of the active layers on the opposite side of the wafer to that from which they have been removed.    USE/ADVANTAGE -   The process allows re-using devices which otherwise would be scrapped. This represents a yield improvement and involves technically simple processing steps.